Method to produce a metal strip, and production plant implementing said method

Abstract

Method to produce metal strip that comprises the casting of a cast product through a casting machine provided with a crystallizer to obtain a slab, and the hot rolling of the slab in a rolling station to obtain metal strip. The casting machine, during casting, exerts an action of reducing the thickness of the cast product exiting the crystallizer.

1 . Method to produce metal strip comprising the casting of a cast product through a casting machine provided with a crystallizer to obtain a slab, and the hot rolling of said slab in a rolling station to obtain metal strip having different strip thicknesses, wherein said casting machine, during casting, exerts an action of reducing the thickness of the cast product exiting the crystallizer, wherein said casting machine is selectively set, as said strip thicknesses vary, in order to exert a different action of reducing the thickness of the cast product, that is, given the same sizes of the crystallizer, at least a first step of producing a first strip having a first thickness, wherein the casting machine exerts a first thickness reduction ratio of the cast product, and at least a second step of producing a second strip having a second thickness, less than the first thickness, wherein the casting machine exerts a second thickness reduction ratio of the cast product, different from the first thickness reduction ratio, said thickness reduction ratio being defined as the difference between the thickness of the cast product exiting from the crystallizer and the slab thickness exiting from the casting machine, correlated to the thickness of the cast product exiting from the crystallizer. 
     
     
         2 . Method as in  claim 1 , wherein the first thickness reduction ratio is less than the second thickness reduction ratio. 
     
     
         3 . Method as in  claim 1 , wherein said casting machine is selectively set to exert an action of reducing the thickness of the cast product exiting from the crystallizer, defined by the formula:
     TAUA=K·A·H   −1   ·e   a·SN      where:   K: is a variable parameter between 0.8 and 1.1;   A: is a coefficient equal to about 4689;   H: is the thickness of the cast product exiting from the crystallizer;   a: is a coefficient equal to −0.37;   SN: is the thickness of the strip to be obtained at the end of rolling.   
     
     
         4 . Method as in  claim 1 , wherein said casting machine comprises a pre-rolling device with rollers which exerts an action of reducing the thickness of the cast product exiting from the crystallizer by means of pre-rolling with liquid core. 
     
     
         5 . Method as in  claim 4 , wherein said pre-rolling device with rollers is provided with a plurality of opposite rollers between which said cast product passes and said rollers are selectively moved toward/away from each other to exert a selective action of liquid core reduction of the thickness of said cast product. 
     
     
         6 . Method as in  claim 4 , wherein said casting machine comprises a drawing unit which exerts an action of reducing the thickness of the cast product exiting from said pre-rolling device with rollers, by means of solid core rolling of the cast product. 
     
     
         7 . Method as in  claim 6 , wherein the drawing unit is selectively set to exert an action of reducing the thickness of the solid core cast product, defined by the formula:
     TAU 2= Q ·(− B·H   b ·ln  SN+C·H   c )
   where:   Q: is a variable parameter between 0.8 and 1.1;   B: is a first coefficient equal to 10928;   H: is the thickness of the cast product (P) exiting from the crystallizer ( 15   a );   b: is a second coefficient equal to −1.659;   SN: is the thickness of the strip;   C: is a third coefficient equal to 10648;   c: is a fourth coefficient equal to −1.596.   
     
     
         8 . Method as in  claim 6 , wherein the reduction in the thickness of the solid core cast product is applied for strip thicknesses comprised between 0.6 mm and 3.5 mm. 
     
     
         9 . Method as in  claim 1 , further comprising: determining the thickness of said cast product exiting from the crystallizer which is a number comprised between 10 mm and 15 mm more than a nominal slab thickness defined by the formula SBN=PR/OPERATING HOURS/(VC*LN*PS), where PR is the productivity of the plant, VC is a casting speed chosen between 4.5 m/min and 6 m/min, LN is the average width of the strip, and PS is the specific weight of the steel. 
     
     
         10 . Method as in  claim 1 , further comprising: determining a thickness ratio applied by the rolling station calculated as the ratio between the value of the slab thickness entering said rolling station, when the strip of minimum thickness is processed, and the value of said minimum thickness of the strip. 
     
     
         11 . Method as in  claim 10 , further comprising: determining the number of rolling stands of the rolling station, where:
 for a ratio of thicknesses comprised between 4 and 12, four rolling stands are provided;   for a ratio of thicknesses comprised between 12 and 21, five rolling stands are provided;   for a ratio of thicknesses comprised between 21 and 52, six rolling stands are provided;   for a ratio of thicknesses comprised between 52 and 110, seven rolling stands are provided.   
     
     
         12 . Plant for producing metal strip comprising a casting machine provided with a crystallizer configured to cast a cast product and obtain a slab, and a rolling station of said slab to obtain metal strip having different strip thicknesses, wherein said casting machine, during casting, is configured to exert an action of reducing the thickness of the cast product exiting from the crystallizer, wherein said casting machine can be selectively configured, as said strip thicknesses vary, in order to exert a different action of reducing the thickness of the cast product, therefore in order to exert, with the same sizes of the crystallizer, at least a first step of producing a first strip having a first thickness, wherein the casting machine exerts a first thickness reduction ratio of the cast product, and at least a second step of producing a second strip having a second thickness, less than the first thickness, wherein the casting machine exerts a second thickness reduction ratio of the cast product, different from the first thickness reduction ratio, said thickness reduction ratio being defined as the difference between the thickness of the cast product exiting from the crystallizer and the slab thickness exiting from the casting machine, correlated to the thickness of the cast product exiting from the crystallizer. 
     
     
         13 . Method as in  claim 2 , wherein said casting machine is selectively set to exert an action of reducing the thickness of the cast product exiting from the crystallizer, defined by the formula:
     TAUA=K·A·H   −1   ·e   a·SN      where:   K: is a variable parameter between 0.8 and 1.1;   A: is a coefficient equal to about 4689;   H: is the thickness of the cast product exiting from the crystallizer;   a: is a coefficient equal to −0.37;   SN: is the thickness of the strip to be obtained at the end of rolling.   
     
     
         14 . Method as in  claim 13 , wherein said casting machine comprises a pre-rolling device with rollers which exerts an action of reducing the thickness of the cast product exiting from the crystallizer by means of pre-rolling with liquid core. 
     
     
         15 . Method as in  claim 14 , wherein said pre-rolling device with rollers is provided with a plurality of opposite rollers between which said cast product passes and said rollers are selectively moved toward/away from each other to exert a selective action of liquid core reduction of the thickness of said cast product. 
     
     
         16 . Method as in  claim 15 , wherein said casting machine comprises a drawing unit which exerts an action of reducing the thickness of the cast product exiting from said pre-rolling device with rollers, by means of solid core rolling of the cast product. 
     
     
         17 . Method as in  claim 16 , wherein the drawing unit is selectively set to exert an action of reducing the thickness of the solid core cast product, defined by the formula:
     TAU 2= Q ·(− B·H   b ·ln  SN+C·H   c )
   where:   Q: is a variable parameter between 0.8 and 1.1;   B: is a first coefficient equal to 10928;   H: is the thickness of the cast product (P) exiting from the crystallizer ( 15   a );   b: is a second coefficient equal to −1.659;   SN: is the thickness of the strip;   C: is a third coefficient equal to 10648;   c: is a fourth coefficient equal to −1.596.   
     
     
         18 . Method as in  claim 17 , wherein the reduction in the thickness of the solid core cast product is applied for strip thicknesses comprised between 0.6 mm and 3.5 mm. 
     
     
         19 . Method as in  claim 18 , further comprising: determining the thickness of said cast product exiting from the crystallizer which is a number comprised between 10 mm and 15 mm more than a nominal slab thickness defined by the formula SBN=PR/OPERATING HOURS/(VC*LN*PS), where PR is the productivity of the plant, VC is a casting speed chosen between 4.5 m/min and 6 m/min, LN is the average width of the strip, and PS is the specific weight of the steel. 
     
     
         20 . Method as in  claim 19 , further comprising: determining a thickness ratio applied by the rolling station calculated as the ratio between the value of the slab thickness entering said rolling station, when the strip of minimum thickness is processed, and the value of said minimum thickness of the strip.